Vertically aligned mode liquid crystal display with differentiated B cell gap with synergistic properties

ABSTRACT

A thin film transistor array substrate is provided with a gate line assembly, a data line assembly, and thin film transistors. The data line assembly crosses over the gate line assembly while defining pixel regions. A pixel electrode is formed at each pixel region. A color filter substrate is provided with a black matrix, and color filters of red, green and blue are formed at the black matrix at the pixel regions. An overcoat layer covers the color filters, and a common electrode is formed on the overcoat layer with an opening pattern. The thin film transistor array substrate, and the color filter substrates face each other, and a liquid crystal material is injected between the thin film transistor array substrate, and the color filter substrate. The blue color filter has a thickness larger than the red color filter or the green color filter such that the liquid crystal cell gap at the blue color filter is smaller than the liquid crystal cell gap at the red or green color filter.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a vertically aligned mode liquidcrystal display and, more particularly, to a vertically aligned modeliquid crystal display where a pixel region is partitioned into aplurality of micro-domains to obtain wide viewing angle.

(b) Description of the Related Art

Generally, a liquid crystal display has a structure where a liquidcrystal bearing dielectric anisotropy is sandwiched between a colorfilter substrate and a thin film transistor array substrate. The colorfilter substrate has a common electrode, color filters and a blackmatrix, and the thin film transistor array substrate has a thin filmtransistor and a pixel electrode. An electric field is applied to theliquid crystal while being varied in strength, thereby controlling thelight transmission and displaying the desired picture image.

Such a liquid crystal display usually involves narrow viewing angle. Inorder to obtain a wider viewing angle, various techniques have beendeveloped. One such technique involves vertically aligning the liquidcrystal molecules with respect to the substrates while forming openingor protrusion patterns at the pixel electrode and the common electrode.

In an opening pattern formation technique, an opening pattern is formedat the pixel electrode and the common electrode, respectively. Fringefields are formed due to the opening patterns, and the inclineddirection(s) of the liquid crystal molecules is controlled by way of thefringe fields, thereby widening the viewing angle.

In a protrusion formation technique, a protrusion is formed at the pixelelectrode and the common electrode, respectively. The electric fieldformed between the pixel electrode and the common electrode is deformeddue to the protrusions, thereby controlling the inclined direction(s) ofthe liquid crystal molecules.

Furthermore, it is also possible that an opening pattern is formed atthe pixel electrode, while a protrusion is formed at the commonelectrode. Fringe fields are formed due to the opening pattern and theprotrusion, and the inclined directions of the liquid crystal moleculesare controlled by way of the fringe fields, thereby partitioning thepixel region into a plurality of micro-domains.

Meanwhile, in such a vertically aligned (VA) mode liquid crystaldisplay, the variation in light transmission based on voltages isdiffused at the respective wavelengths of light, and this causes theinter-gray scale color shift. Particularly, when the gray scale reachesa higher number the white color becomes yellowish, deteriorating picturequality.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a vertically alignedmode liquid crystal display which enhances picture quality whilereducing color shift.

This and other objects may be achieved by a liquid crystal displaywherein the cell gap at the blue region is differentiated from the cellgap at the red or green region.

According to one aspect of the present invention, the liquid crystaldisplay includes a first insulating substrate, and a first wiring lineassembly formed on the first insulating substrate with a plurality offirst wiring lines. A second wiring line assembly crosses over the firstwiring line assembly with a plurality of second wiring lines whiledefining pixel regions. The second wiring line assembly is insulatedfrom the first wiring line assembly. A pixel electrode is formed at eachpixel region with a first opening pattern. A thin film transistor isconnected to the first wiring line assembly, the second wiring lineassembly, and the pixel electrode. A second insulating substrate facesthe first insulating substrate. Color filters of red, green and blue areformed on the second insulating substrate. A common electrode is formedon the second insulating substrate with the color filters while bearinga second opening pattern. A liquid crystal layer is sandwiched betweenthe first and the second insulating substrates with liquid crystalmolecules. The liquid crystal molecules of the liquid crystal layer arevertically aligned with respect to the first and the second substrateswith no application of an electric field between the pixel electrode andthe common electrode. Assuming that an R cell gap indicates thethickness of the liquid crystal layer at the region of the red colorfilter, a G cell gap indicates the thickness of the liquid crystal layerat the region of the green color filter, and the B cell gap indicatesthe thickness of the liquid crystal layer at the region of the bluecolor filter, the B cell gap is differentiated from the R cell gap orthe G cell gap.

The B cell gap is established to be smaller than the R cell gap or the Gcell gap by 0.2±0.15 μm. The B cell gap, the R cell gap and the G cellgap may be differentiated from each other while satisfying the followingmathematical formula: R cell gap−G cell gap<G cell gap−B cell gap.

The first and the second opening patterns partition the pixel regioninto a plurality of micro-domains. The micro-domains are classified intoleft and right domains, and upper and lower domains. The volume occupiedby the upper and lower domains is larger than the volume occupied by theleft and right domains. The distance between the two neighboring secondwiring lines is repeatedly varied per a predetermined length, and thepixel electrode has lateral sides positioned close to the second wiringlines with the same outline such that the pixel electrode bears a narrowportion and a wide portion.

According to another aspect of the present invention, a color filtersubstrate for the liquid crystal display includes an insulatingsubstrate, and a black matrix formed on the insulating substrate whiledefining pixel regions. Color filters of red, green and blue are formedat the pixel regions. An overcoat layer covers the color filters. Atransparent electrode is formed on the overcoat layer with an openingpattern. The blue color filter has a thickness larger than the red colorfilter or the green color filter. Preferably, the thickness of the bluecolor filter is larger than the red color filter or the green colorfilter by 0.2±0.15 μm.

According to still another aspect of the present invention, a process ofmanufacturing a liquid crystal display is provided, comprising the stepsof: forming a first insulating substrate; forming a first wiring lineassembly with a plurality of first wiring lines on the first insulatingsubstrate; forming a second wiring line assembly with a plurality ofsecond wiring lines crossing over the first wiring line assembly whiledefining pixel regions, the second wiring line assembly being insulatedfrom the first wiring line assembly; forming a pixel electrode at eachpixel region with a first opening pattern; forming a second insulatingsubstrate facing the first insulating substrate; forming color filtersof red, green and blue on the second insulating substrate; forming acommon electrode on the second insulating substrate with the colorfilters having a second opening pattern; forming a liquid crystal layersandwiched between the first and the second insulating substrates withliquid crystal molecules, the liquid crystal molecules of the liquidcrystal layer being vertically aligned with respect to the first and thesecond substrates when no electric field is applied between the pixelelectrode and the common electrode; and differentiating a B cell gapfrom an R cell gap or a G cell gap, the R cell gap indicates thethickness of the liquid crystal layer at the region of the red colorfilter, the G cell gap indicates the thickness of the liquid crystallayer at the region of the green color filter, and the B cell gapindicates the thickness of the liquid crystal layer at the region of theblue color filter. Preferably, the B cell gap is formed to be smallerthan the R cell gap or the G cell gap by 0.2±0.15 μm and at least one ofthe first and second opening patterns partitions the pixel region into aplurality of micro-domains.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or the similar components, wherein:

FIG. 1 is a plan view of a liquid crystal display according to a firstpreferred embodiment of the present invention where an opening patternof a pixel electrode is illustrated;

FIG. 2 illustrates an opening pattern of a common electrode for theliquid crystal display shown in FIG. 1;

FIG. 3 illustrates the arrangement of the opening patterns of the pixeland the common electrodes for the liquid crystal display shown in FIG.1;

FIG. 4 is a cross sectional view of the liquid crystal display takenalong the IV–IV′ line of FIG. 3;

FIG. 5 is a plan view of a liquid crystal display according to a secondpreferred embodiment of the present invention where an opening patternof a pixel electrode is illustrated;

FIG. 6 illustrates an opening pattern of a common electrode for theliquid crystal display shown in FIG. 5;

FIG. 7 illustrates the arrangement of the opening patterns of the pixeland the common electrodes for the liquid crystal display shown in FIG.5;

FIG. 8 is a cross sectional view of the liquid crystal display takenalong the VIII–VIII′ line of FIG. 7;

FIG. 9 is a graph illustrating the difference in light transmission as afunction of Δn·d at the wavelengths of 450 nm and 600 nm;

FIG. 10 is a graph where the values at the vertical axis of the graph ofFIG. 9 are divided by the light transmission at the wavelength of 550nm;

FIG. 11 is a graph illustrating the optimum RGB cell gaps in case thevalue of Δn is 0.08;

FIGS. 12A to 12C are graphs illustrating the V-T curves pursuant to theRGB cell gaps;

FIG. 13 is a graph illustrating the difference in the V-T curve at thesingle-domain structure and at the multi-domain structure;

FIG. 14 is a graph illustrating the amount of color shift pursuant tothe difference in cell gap at the yellow region (the average between thered region and the green region) and at the blue region;

FIG. 15 is a graph illustrating the brightness ratio (blue/yellow)pursuant to the difference in cell gap between the yellow region and theblue region;

FIG. 16 is a graph illustrating the difference in color temperature pergray scales pursuant to the difference in cell gap between the yellowregion and the blue region; and

FIG. 17 is a graph illustrating the color property, and processingefficiency and variation in yield as a function of cell gaps.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of this invention will be explained with referenceto the accompanying drawings.

FIG. 1 is a plan view of a liquid crystal display according to a firstpreferred embodiment of the present invention wherein an opening patternof a pixel electrode is illustrated, and FIG. 2 illustrates an openingpattern of a common electrode for the liquid crystal display. FIG. 3illustrates the arrangement of the opening patterns of the pixel and thecommon electrodes for the liquid crystal display. FIG. 4 is a crosssectional view of the liquid crystal display taken along the IV–IV′ lineof FIG. 3.

As shown in FIG. 1 to FIG. 4 of the drawings, a gate line assembly and astorage capacitor line assembly are formed on an insulating substrate10. The gate line assembly includes gate lines 20 arranged along ahorizontal direction, and gate electrodes 21 protruded from the gatelines 20. The storage capacitor line assembly includes storage capacitorlines 30 arranged along the horizontal direction substantially parallelto the gate lines 20. First to fourth storage capacitor electrodes 31 to34 are branched from the storage capacitor line 30 together with storagecapacitor electrode connectors 35 and 36. The first storage capacitorelectrode 31 is directly connected to the storage capacitor line 30while proceeding in the vertical direction. The second and the thirdstorage capacitor electrodes 32 and 33 are connected to the firststorage capacitor electrode 31 while proceeding in the horizontaldirection. The fourth storage capacitor electrode 34 is connected to thesecond and the third storage capacitor electrodes 32 and 33 whileproceeding in the vertical direction. The storage capacitor electrodeconnectors 35 and 36 interconnect the fourth storage capacitor electrode34 at one pixel and the first storage capacitor electrode 31 at aneighboring pixel.

A gate insulating layer 40 is formed on the gate line assembly and thestorage capacitor line assembly. A semiconductor pattern 50 is formed onthe gate insulating layer 40 over the gate electrodes 21 with amorphoussilicon. Ohmic contact patterns 61 and 62 (not shown) are formed on thesemiconductor pattern 50 with amorphous silicon where n type impuritiessuch as phosphorous (P) are doped at high concentration. The ohmiccontact patterns 61 and 62 are separated from each other around the gateelectrode 21.

A data line assembly is formed at the substrate 10. The data lineassembly includes source electrodes 71 formed on the one-sided ohmiccontact pattern 61, drain electrodes 72 formed on the other-sided ohmiccontact pattern 62, and data lines 70 formed on the gate insulatinglayer 40 while proceeding in the vertical direction. The sourceelectrodes 71 are connected to the data lines 70.

A protective layer 80 is formed on the data line assembly with contactholes 81 exposing the drain electrodes 72. Pixel electrodes 90 areformed on the protective layer 80 such that they are connected to thedrain electrodes 72 through the contact holes 81. The pixel electrodes90 are formed with a transparent conductive material such as indium tinoxide (ITO) and indium zinc oxide (IZO).

The pixel electrode 90 is separated into first to third electrodeportions 91 to 93, and the first to third electrode portions 91 to 93are connected to each other by way of connectors 94 to 96. The firstelectrode portion 91 is formed at the lower half side of the pixelregion with a rectangular shape with four corner edges cut off. Thefirst electrode portion 91 is connected to the drain electrode 72through the contact hole 81. The second and the third electrode portions92 and 93 are formed at the upper half of the pixel region, each alsohaving a rectangular shape with four corner edges cut off. The secondelectrode portion 92 is connected to the first electrode portion 91 byway of the first and the second connectors 94 and 96, and the thirdelectrode portion 93 is connected to the second electrode portion 92 byway of the third connector 95.

The second storage capacitor electrode 32 is positioned between thefirst and the second electrode portions 91 and 92. The third storagecapacitor electrode 33 is positioned between the second and the thirdelectrode portions 92 and 93. The first and the fourth storage capacitorelectrodes 31 and 34 are positioned between the pixel electrode 90 andthe neighboring data lines 70, respectively.

Each of the first to the third electrode portions 91 to 93 has a firstside proceeding parallel to the data lines 70, and a second sideproceeding parallel to the gate lines 20. The first side of the firstelectrode portion 91 is longer than the second side thereof. The firstside of the second and the third electrode portions 92 and 93 is shorterthan the second side thereof. The second and the third electrodeportions 92 and 93 are overlapped with the first and the fourth storagecapacitor electrodes 31 and 34, whereas the first electrode portion 91is not overlapped with the first and the fourth storage capacitorelectrodes 31 and 34. The storage capacitor line 30 is positionedbetween the gate line 20 and the third electrode portion 93. An electricpotential to be applied to a common electrode of a color filtersubstrate would be also applied to the storage capacitor lines 30, thestorage capacitor electrodes 31 to 34, and the storage capacitorelectrode connectors 35 and 36.

As described above, when the storage capacitor lines or the storagecapacitor electrodes to be applied with a common electric potential arearranged between the data line and the pixel electrode or between thegate line and the pixel electrode, they prevent the electric field atthe pixel region from being influenced by the data line electricpotential and the gate line electric potential, thereby securing domainstability.

A color filter substrate for the liquid crystal display will beexplained with reference to FIGS. 2 to 4.

As shown in the drawings, a black matrix 200 is formed on a transparentglass substrate 100 while defining the pixel regions. The black matrix200 preferably includes a double-layered structure with a chrome-basedlayer and a chrome oxide-based layer. Color filters of red (R), green(G) and blue (B) 310, 320 and 330 are formed at the pixel regions. Thecolor filters are different in thickness. Preferably, the thickness ofthe R color filter 310 is smaller than that of the G color filter 320,that is in turn smaller than that of the B color filter 330. Thisthickness differentiation is to make the cell gap differ at therespective pixel regions. An overcoat layer 600 covers the RGB colorfilters 310, 320 and 330 to protect them, and a common electrode 400 isformed on the overcoat layer 600 with a transparent conductive material.An opening pattern is formed on the common electrode 400 at each pixelregion with first to third opening portions 410, 420 and 430. The firstopening portion 410 bisects the lower half of the pixel region in thehorizontal direction, and the second and the third opening portions 420and 430 trisect the upper half of the pixel region in the verticaldirection. Both ends of each opening portion 410, 420 or 430 aregradually enlarged to form a triangular shape, preferably an isoscelestriangle. The first to third opening portions 410, 420 and 430 areseparated from each other.

The thin film transistor array substrate is combined with the colorfilter substrate, and a liquid crystal material 900 is injected betweenthe substrates. At this time, the directors of the liquid crystalmolecules are vertically aligned with respect to the substrates. Twopolarizing plates 11 and 101 are externally attached to the substrates10 and 100 such that the polarizing axes thereof are perpendicular toeach other.

In this state, the electrode portions 91 to 93 of the pixel electrode 90and the first to third opening portions 410 to 430 of the commonelectrode 400 are overlapped with each other while partitioning thepixel region into a plurality of micro-domains. Each of the electrodeportions 91 to 93 of the pixel electrode 90 has two long sides and twoshort sides, and the long sides of each electrode portion proceed in adirection parallel to the data lines 70 or the gate lines 20 while beinginclined with respect to the polarizing axes of the polarizing plates by45°.

In case the long side of each electrode portion is positioned close tothe data lines 70 or the gate lines 20, the storage capacitor lines 30or the storage capacitor electrodes 31 to 34 are arranged between thedata lines 70 and the long sides of the electrode portion, or betweenthe gate lines 20 and the long sides of the electrode portion.

Meanwhile, it is preferable that the storage capacitor line assembly benot disposed close to the short sides of the electrode portions 91 to 93of the pixel electrode 90. In a case wherein the storage capacitor lineassembly was disposed there, it would be entirely covered by the pixelelectrode 90, or positioned distant from the pixel electrode 90 by 3 μmor more. This is because the electric potential of the data lines 70 orthe gate lines 20 works in the direction of obstructing the domainformation at the place where the data lines 70 or the gate lines 20 ispositioned close to the long sides of the pixel electrode portions 91 to93, whereas the electric potential of the data lines 70 or the gatelines 20 works in the direction of helping the domain formation at theplace where the data lines 70 or the gate lines 20 is positioned closeto the short sides of the pixel electrode portions 91 to 93.

Meanwhile, the liquid crystal material 900 is injected between thecommon electrode 400 and the pixel electrodes 91. As described above,since the RGB color filters 310 to 330 are differentiated in thickness,the distance between the common electrode 400 and the pixel electrode 90is differentiated at the RGB pixel regions. That is, the cell gap isdifferentiated at the RGB pixel regions. The R cell gap at the R pixelregion is larger than the G cell gap at the G pixel region that is inturn larger than the B cell gap at the B pixel region. The B cell gap issmaller than the average value of the R cell gap and the G cell gap by0.2±0.15 μm. Furthermore, the difference Δd₂ between the G cell gap andthe B cell gap is greater than the difference Δd₁ between the R cell gapand the G cell gap. That is, Δd₁<Δd₂. In case the RGB cell gaps aredifferentiated, the inter-gray scale color shift can be reduced.

FIG. 5 is a plan view of a liquid crystal display according to a secondpreferred embodiment of the present invention wherein an opening patternof a pixel electrode is illustrated, and FIG. 6 illustrates an openingpattern of a common electrode for the liquid crystal display. FIG. 7illustrates the arrangement of the opening patterns of the pixel and thecommon electrodes for the liquid crystal display. FIG. 8 is a crosssectional view of the liquid crystal display taken along the VIII–VIII′line of FIG. 7.

As shown in FIGS. 5 to 8 of the drawings, a gate line assembly and astorage capacitor line assembly are formed on an insulating substrate10. The gate line assembly includes gate lines 20 proceeding in ahorizontal direction, and gate electrodes 21 protruded from the gatelines 20. The storage capacitor line assembly includes storage capacitorlines 30 proceeding in the same direction as the gate lines 20. Thestorage capacitor line 30 has a plurality of linear portions with alarge width and connectors interconnecting the linear portions having asmaller width. The linear portions are arranged around an imaginativestraight line up and down in an alternate manner. First and secondstorage capacitor electrodes 33 and 31 are connected to the storagecapacitor line 20 while proceeding in a vertical direction, and thirdstorage capacitor electrodes 32 are connected to the second storagecapacitor electrode 31 while proceeding in the horizontal direction.

A gate insulating layer 40 is formed on the gate line assembly and thestorage capacitor line assembly.

A semiconductor pattern 50 is formed on the gate insulating layer 40with hydrogenated amorphous silicon such that it is overlapped with thegate electrodes 21.

Ohmic contact patterns (not shown) are formed on the semiconductorpattern 50 with n+ hydrogenated amorphous silicon where n-typeimpurities are doped at high concentration. The ohmic contact patternsare separated from each other around the gate electrode 21.

A data line assembly is formed on the gate insulating layer 40. The dataline assembly includes data lines 70 formed on the gate insulating layer40 while proceeding in the vertical direction. The data line 70 has aplurality of linear portions, and connectors interconnecting the linearportions. The linear portions are arranged around an imaginativestraight line left and right in an alternate manner. The distancebetween the neighboring linear portions placed around the imaginativestraight line up and down or left and right is controlled inconsideration of the occupation ratios of upper and lower domains, andleft and right domains. As the neighboring data lines 70 are opposite toeach other in the alternating order of the linear portions, narrow andwide regions are alternately present between the data lines 70. Thisstructure is the same in the left and right directions as well as in theupper and lower directions. The data lines 70 are overlapped with thestorage capacitor lines 30 and the gate lines 20. The overlapping of thedata lines 70 and the storage capacitor lines 30 is made at theconnectors thereof.

A protective layer 80 is formed on the data lines 70. A pixel electrode90 is formed on the protective layer 80 at each pixel region with indiumtin oxide (ITO) or indium zinc oxide (IZO). The pixel electrode 90 isconnected to the drain electrode 72 through the contact hole 81. Thepixel electrode 90 has a wide portion, and a narrow portion.Furthermore, the pixel electrode 90 bears an opening pattern. Theopening pattern includes a first opening portion 98 formed at the narrowportion of the pixel electrode 90 along the vertical direction, andsecond opening portions 99 formed at the wide portion of the pixelelectrode 90 along the horizontal direction. The narrow portion of thepixel electrode 90 is bisected by the first opening portion 98 left andright, and the wide portion of the pixel electrode 90 is trisected intoa top domain, a middle domain and a bottom domain by way of the secondopening portions 99. The middle domain has a width about two timesgreater than the top and the bottom domains. The first opening portion98 is overlapped with the first storage capacitor electrode 33, and thesecond opening portions 99 are overlapped with the third storagecapacitor electrodes 32.

A color filter substrate facing the thin film transistor array substratewill be explained with reference to FIGS. 6 and 8.

A black matrix 200 is formed on an insulating substrate 100, and RGBcolor filters 310, 320 and 330 are formed at the black matrix 200. The Bcolor filter 320 has a thickness larger than the R or G color filter 310or 320. This is to make the cell gap at the B pixel region smaller thanthe cell gap at the R or G pixel region. An overcoat layer 600 is formedon the color filters 310, 320 and 330, and a common electrode 400 isformed on the overcoat layer 600 with a transparent conductive materialsuch as ITO and IZO. An opening pattern similar to that shown in FIG. 8is formed at the common electrode 400. The opening pattern is formedwith third opening portions 410 longitudinally proceeding in thevertical direction, and fourth and fifth opening portions 420 and 430longitudinally proceeding in the horizontal direction. In the entirepixel structure, the set of the fourth and fifth opening portions 420and 430 is positioned at the left and right sides of the set of thethird opening portions 410, respectively. The boundary of the thirdopening portion 410 close to the fourth and the fifth opening portions420 and 430 is hollowed such that it can be separated from the fourthand the fifth opening portions 420 and 430.

The thin film transistor array substrate 10 is combined with the colorfilter substrate 100 such that they are spaced apart from each otherwith a predetermined distance. A liquid crystal material is injectedbetween the substrates 10 and 100 to form a liquid crystal layer 900,and sealing is made thereto. With no application of an electric fieldbetween the pixel electrode 90 and the common electrode 400, thedirectors of the liquid crystal molecules are vertically aligned withrespect to the substrates 10 and 100.

The liquid crystal layer 900 is sandwiched between the common electrode400 and the pixel electrode 91. Since the thickness of the B colorfilter 330 is larger than the R or G color filter 310 or 320, thedistance between the common electrode 400 and the pixel electrode 90 atthe B pixel region is smaller than that at the R or G pixel region. Thatis, the B cell gap at the B pixel region is smaller than the R cell gapat the R pixel region or the G cell gap at the G pixel region. The Bcell gap is smaller than the R or G cell gap by 0.2±0.15 μm. That is,Δd₃=0.2±0.15 μm. In case the RGB cell gaps are differentiated, theinter-gray scale color shift is reduced.

In the combination state of the thin film transistor array substrate 10and the color filter substrate 100, the third opening portions 410 areoverlapped with the left and right sides of the narrow pixel electrodeportion 90, and the fourth opening portions 420 are overlapped with theupper and lower boundaries of the wide pixel electrode portion 90. Thefifth opening portion 430 is positioned at the wide portion of the pixelelectrode 90 such that the former bisects the latter vertically or upand down. Accordingly, the narrow portion of the pixel electrode 90 ispartitioned into two micro-domains by way of the first opening portion98 and the third opening portions 410. The wide portion of the pixelelectrode 90 is partitioned into four micro-domains by way of the secondopening portions 99, and the fourth and fifth opening portions 420 and430. It is preferable that the width of the micro-domain be 20±5 μm. Thewidth of the micro-domain is determined in consideration of theoccupation ratios of the upper and lower domains B and the left andright domains A. When the width of the micro-domain is too narrow, theopening ratio is reduced. When the width of the micro-domain is toowide, the fringe field formation is too weak to control the incliningdirection of the liquid crystal molecules. Furthermore, the occupationratio of the upper and lower domains B may be established to be greaterthan the left and right domains A. It is preferable that the occupationratio of the upper and lower domains B be 60–90% of the entire pixelregion. In this way, the visibility at the left and right sides can beenhanced.

The above-structured opening patterns serves to significantly enhancethe opening ratio. The resulting liquid crystal display bears an openingratio of 48%. This can be done through varying the shape of the pixelelectrode such that the upper and lower domains and the left and rightdomains thereof can be controlled in an appropriate manner. Furthermore,the opening pattern formed at the common electrode is positioned at theperiphery of each pixel region that is screened by the black matrix 200.The third opening portions 410 are overlapped with the left and rightsides of the narrow pixel electrode portion 90, and the fourth openingportions 420 are overlapped with the upper and lower boundaries of thewide pixel electrode portion 90. That is, the opening pattern ispositioned at the place screened by the black matrix 200, or where thestorage capacitor lines 30 are positioned. Therefore, the third andfourth opening portions 410 and 420 do not cause additionaldeterioration in the opening ratio.

In the liquid crystal display according to the second preferredembodiment, all of the micro-domains are rectangularly shaped toadvantageously provide improved speed response and minimize textureoccurrence at the edges of the micro-domains. The inter-gray scale colorshift is reduced through differentiating the RGB cell gaps can be seenin the following data and analysis.

FIG. 9 is a graph illustrating the difference in light transmission as afunction of Δnd at the wavelengths of 450 nm and 600 nm, and FIG. 10 isa graph where the values of the vertical axis of the graph of FIG. 9 aredivided by the light transmission at the wavelength of 550 nm. In thegraphs, as the values of Δn·d where the light transmission is maximizedat the TN and VA modes are 0.27 nm and 0.47 nm, the values of Δn·d aredivided by 0.27 nm and 0.47 nm to normalize them.

As known from the graph of FIG. 9, in the VA or TN mode liquid crystaldisplay, the variation in Δn·d causes the difference in lighttransmission at the wavelengths of 450 nm and 600 nm. This means thatthe increasing degree in the light transmission due to the increase inn·d differs at the wavelength of 450 nm, and at the wavelength of 600nm. The reason is explained below.

The mathematical formula for determining the light transmission T at theTN mode is expressed by equation 1.T=1−(sin²(π/2√(1+u ²)))/(1+u ²), u=2dΔn/λ  (1)

The mathematical formula for determining the light transmission T at theVA mode is expressed by equation 2.T=sin²((π/2)u), u=2dΔn/λ  (2)

Meanwhile, the value of dΔn is altered depending upon variation in thevoltage applied between the common electrode and the pixel electrode.That is, the liquid crystal molecules vertically aligned with respect tothe substrates are inclined under the application of voltage so that theeffective value of dΔn is increased. However, as known from theequations 1 and 2, the value of T is varied depending upon the value ofu, that is in turn varied depending upon the values of dΔn and λ. As thevalue of T is varied depending upon the values of dΔn and λ, it isinfluenced by variation in the wavelength λ. Accordingly, T hasdiffusion characteristics at the respective wavelengths.

As known from the graph of FIG. 9, in the TN and VA modes, the lighttransmission with the shorter wavelengths is high at middle gray scales.This inclination is stronger in the VA mode than in the TN mode.Therefore, the inter-gray scale color shift phenomenon becomes moresevere in the VA mode than in the TN mode.

As known from the graph of FIG. 10, the B color bearing a shortestwavelength exhibits high light transmission at lower gray scales, andthe light transmission of the R and G colors is gradually heightened athigher gray scales. Accordingly, the yellow content where the R colorand the G color are combined is increased and the yellowish phenomenonis seen.

This situation can be improved through controlling the RGB cell gaps. Inthe equation 2, in order that the value of T is not influenced by thewavelength of λ while being dependent upon only the value of Δn variedin accordance with the inclining degree of the liquid crystal molecules,equation 3 should be satisfied.d=kλ  (3)where k is a constant number.

In the case of a liquid crystal where the maximum value of Δn is 0.08,it is preferable in the aspect of brightness that the value of T inequation 2 should be maximized when Δn=0.08.

The value of T is maximized whenu=1. When u=1, the second formula inequation 2 becomes 1=2dΔn/λ. In view of equation 3 and Δn=0.08,1=2kΔn=2k×0.08. Therefore, k=1/0.16.

When k is applied to equation 3, equation 4 is obtained.d=λ/0.16  (4)

Assuming that the RGB wavelengths are 0.65 μm, 0.55 μm and 0.45 μm, theRGB cell gaps d should be 4.06 μm, 3.44 μm and 2.81 μm, respectively toeradicate the inter-gray scale color shift.

FIG. 11 is a graph illustrating the optimum RGB cell gaps when themaximum value of Δn is 0.08.

Meanwhile, the cell gaps d at the RGB pixel regions can be most easilycontrolled through controlling the thickness of the RGB color filters.However, as is known and can be seen from the graph of FIG. 11, thedifference in the R and B cell gaps required to eradicate the inter-grayscale color shift reaches about 1.25. At such level, it becomesdifficult in processing and making such a difference through controllingthe thickness of the color filters. Furthermore, it is difficult toobtain uniformity in the cell gaps, making it nearly impossible toemploy such a technique for practical use.

Therefore, a technique of easily making the cell gap difference in apractical manner while being effective in reduction of the inter-grayscale color shift is needed.

FIGS. 12A to 12C are graphs illustrating the V-T curves pursuant to theRGB cell gaps.

As known from the graphs, with variation in the cell gaps, the shape ofthe VT curve is most affected at the B color region. That is, since theshape of the VT curve is most sensitively altered at the B color regiondepending upon the variation in cell gap close to 4.0 μm, it would bemost effective to control the cell gap at the B color region.

Meanwhile, in a patterned vertically aligned (PVA) mode where an openingpattern is formed at the electrode components to obtain wide viewingangle, as the electric field is weaker at the opening area than at thenon-opening area, the effective value of n·d of the liquid crystal issmall. Therefore, in the entire pixel structure, the VT curve related tothe PVA mode is smoothly elevated compared to the VA or TN mode wherethe opening pattern is absent.

FIG. 13 is a graph illustrating the difference in the V-T curve at thesingle-domain structure and at the multi-domain structure. As describedearlier, the VT curve at the multi-domain structure where an openingpattern is present is smoothly elevated compared to that at thesingle-domain structure where such an opening pattern is absent. Thisprovides an effect of self-correcting the color shift. In the case ofthe PVA mode, even an extremely small cell gap difference, such as adifference less than the theoretically computed cell gap difference of1.25 μm may induce an effect of considerable reduction in the colorshift.

FIG. 14 is a graph illustrating the amount of color shift due to thedifference in cell gap at the yellow region (the average between the redregion and the green region) and at the blue region. FIG. 15 is a graphillustrating the brightness ratio (blue/yellow) due to the difference incell gap between the yellow region and the blue region. FIG. 16 is agraph illustrating the difference in color temperature per gray scalesdue to the difference in cell gap between the yellow region and the blueregion.

It can be seen from the graphs of FIGS. 14 and 15 that the inter-grayscale color shift is significantly reduced even when the B cell gap atthe blue pixel region is smaller than the R or G cell gap at the red orgreen pixel region by 0.2–0.3 μm. This is because the variation in the Bcell gap largely influences the color shift, and in the case of a PVAmode, the color shift is self-corrected due to the opening pattern.

FIG. 17 is a graph illustrating the color property, and processingefficiency and variation in yield as a function of cell gaps.

As shown in the graph of FIG. 17, the color property is improved whenthe cell gap difference is approximately 1.25 or higher. But theprocessing efficiency and the yield are lowered when the cell gapdifference is increased. Accordingly, the B cell gap is established tobe smaller than the R or G cell gap by 0.2±0.15 μm . In this condition,the color property is good, and the desired processing efficiency oryield is obtained.

As described above, when the B cell gap is established to be smallerthan the R or G cell gap by 0.2±0.15 μm, the inter-gray scale colorshift can be reduced, and the resulting display device can exhibit goodpicture quality. Furthermore, the G cell gap may be smaller than the Rcell gap such that the RGB cell gaps are all differentiated from eachother. In such case, it is preferable that the difference between the Rand G cell gaps be smaller than the difference between the G and B cellgaps. This is because, as shown from the graphs of FIGS. 12A to 12C, thevariation in the B cell gap can induce greater effects.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A liquid crystal display comprising: a first insulating substrate; afirst wiring line assembly formed on the first insulating substrate witha plurality of first wiring lines; a second wiring line assemblycrossing over the first wiring line assembly with a plurality of secondwiring lines while defining pixel regions, the second wiring lineassembly being insulated from the first wiring line assembly; a pixelelectrode formed at each pixel region with a first opening pattern; athin film transistor connected to the first wiring line assembly, thesecond wiring line assembly, and the pixel electrode; a secondinsulating substrate facing the first insulating substrate; colorfilters of red, green and blue formed on the second insulatingsubstrate; a common electrode formed on the second insulating substratewith the color filters having a second opening pattern; and a liquidcrystal layer sandwiched between the first and the second insulatingsubstrates with liquid crystal molecules, the liquid crystal moleculesof the liquid crystal layer being vertically aligned with respect to thefirst and the second substrates when no electric field is appliedbetween the pixel electrode and the common electrode; wherein a B cellgap is differentiated from an R cell gap or a G cell gap, the R cell gapindicates the thickness of the liquid crystal layer at the region of thered color filter, the G cell gap indicates the thickness of the liquidcrystal layer at the region of the green color filter, and the B cellgap indicates the thickness of the liquid crystal layer at the region ofthe blue color filter, wherein the B cell gap, the R cell gap and the Gcell gap are differentiated from each other by: R cell gap−G cell gap<Gcell gap−B cell gap, and wherein the first and the second openingpatterns partition the pixel region into a plurality of micro-domains.2. The liquid crystal display of claim 1 wherein the B cell gap isestablished to be smaller than the R cell gap or the G cell gap by0.2±0.15 μm.
 3. The liquid crystal display of claim 1 wherein themicro-domains are classified into left and right domains, and upper andlower domains, the volume occupied by the upper and lower domains beinglarger than the volume occupied by the left and right domains.
 4. Theliquid crystal display of claim 1 wherein the distance between twoneighboring second wiring lines is repeatedly varied per a predeterminedlength, and the pixel electrode has lateral sides positioned close tothe second wiring lines with the same outline such that the pixelelectrode bears a narrow portion and a wide portion, and wherein a lineformed of points that have the same distance from the two neighboringsecond wiring lines is substantially a straight line.
 5. A process ofmanufacturing a liquid crystal display, comprising the steps of: forminga first insulating substrate; forming a first wiring line assembly witha plurality of first wiring lines on the first insulating substrate;forming a second wiring line assembly with a plurality of second wiringlines crossing over the first wiring line assembly while defining pixelregions, the second wiring line assembly being insulated from the firstwiring line assembly; forming a pixel electrode at each pixel regionwith a first opening pattern; forming a second insulating substratefacing the first insulating substrate; forming color filters of red,green and blue on the second insulating substrate; forming a commonelectrode on the second insulating substrate with the color filtershaving a second opening pattern; forming a liquid crystal layersandwiched between the first and the second insulating substrates withliquid crystal molecules, the liquid crystal molecules of the liquidcrystal layer being vertically aligned with respect to the first and thesecond substrates when no electric field is applied between the pixelelectrode and the common electrode; and differentiating a B cell gapfrom an R cell gap or a G cell gap, the R cell gap indicates thethickness of the liquid crystal layer at the region of the red colorfilter, the G cell gap indicates the thickness of the liquid crystallayer at the region of the green color filter, and the B cell gapindicates the thickness of the liquid crystal layer at the region of theblue color filter, wherein the B cell gap, the R cell gap and the G cellgap are differentiated from each other by: R cell gap−G cell gap<G cellgap−B cell gap, and wherein at least one of the first and second openingpatterns partitions the pixel region into a plurality of micro-domains.6. The process of manufacturing according to claim 5 wherein the B cellgap is formed to be smaller than the R cell gap or the G cell gap by0.2±0.15 μm.